1. Field of the Invention
The present invention relates to a detecting method for a Liquid Crystal Display (LCD), and in particular to a method for detecting line broken fault of common electrode lines of the LCD.
2. Discussion of the Background
A Liquid Crystal Display (LCD) having such features as small volume, low power consumption and no radiation is now occupied the leading position in the field of flat panel display. The main body structure of liquid crystal display comprises a array substrate and a color filter substrate paired each other and having a liquid crystal interposed therebetween, wherein a gate line providing scan signal, a data line providing data signal, a pixel electrode forming the pixel dot and common electrode lines providing common voltages are formed over the array substrate, and black matrix and color resin are formed on the color filter substrate.
In order to ensure the quality of the product, after the liquid crystal display is formed by pairing the array substrate and the color filter substrate, it need to make a gray picture detection so as to detect the related defects and make appropriate repairs. Defects in liquid crystal display include pixel dots fault and line broken fault, while the line broken fault is further classified as line broken fault of gate lines, line broken fault of data lines and line broken fault of common electrode lines. It shows from the utility in practice that it is difficult for the picture detection method in the related art to detect the line broken fault of common electrode lines, which results in not only the waste of the raw materials in the subsequent process, but also results the quality degradation when used by the consumer.
FIG. 10 is a schematic diagram illustrating a structure of the common electrode lines on the array substrate in the related art, which is a typical array substrate structure of a storage Capacitor On Common electrode line (Cst On Common), and the common electrode line is of mesh structure. The mesh structure of the common electrode line is a structure commonly adopted in the related art, especially for the product with a big size, in order to make the common electrode signal more uniform, the common electrode adopted a form of inputting from two ends. It is appreciated that the voltages at any point on the common electrode line with the mesh structure are equal to a common electrode voltage Vcom externally applied on the common electrode line. As shown in FIG. 10, common electrode line 1 overlaps with pixel electrode 2, and the storage capacitor is formed at each overlapped place. In operation, common electrode voltage Vcom is not equal to the pixel electrode voltage Vpx1 applied on the pixel electrode. A part of the electronic charge would charge the storage capacitor according to the capacitor effect due to the existing of the storage capacitor, which causes the change in the voltage along with the common electrode line. When line broken occurs at some point at the common electrode line, the transmission mechanism of both ends of the common electrode line is destroyed at the line broken, and the common electrode signal on the common electrode line with line broken would introduce difference as compared with that of other common electrode line without line broken. In particular, as for a product of a liquid crystal screen with m pixels (m is a positive integer) in one direction of the common electrode line, it is assumed that line broken happens at the n-th pixel (n is an positive integer, n<m) in one common electrode line, that is, signals of both sides at the line broken of the common electrode line are transmitted through a single end, wherein the load of the longer end has a length of n (assuming m/2<n) pixels, while the load of both side of the normal common electrode line could be considered as m/2 since it uses the signal transmission mechanism of two ends; therefore a difference is generated between the common electrode line with line broken and the normal common electrode line. However, in fact, under various detection of gray picture in the prior art, the detected picture difference caused by the line broken of common electrode line is very small, even unable to be recognized.